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33 Cards in this Set

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  • Back
the two reasons we need eye movement are...
bc the fovea is the only place for high accuity vision, and both eyes must be precisely co-alligned so that they can be fused for stereoscopic vision
what muscles are required for intortion? extortion?
superior rectus and superior oblique; inferior rectus and inferior oblique
cortical control of the eye movement is exerted by what fibers from the cortex? These fibers then project to where?
corticobulbar fibers; to brainstem centers, particularly the superior colliculi and the gaze centers (areas of reticular formation that program eye movement)
what gaze center moves both eyes to the same side at the same time? what is the path of its fibers?
the lateral gaze centers AKA PPRF or abducens; it is found in the brainstem RF at the level of the facial colliculus (the pons) and it sends fibers to the ipsilateral abducens nucleus and contralateral occulomotor nucleus (via the medial longitudinal fasciculus for occulomotr nucleus). Note that antagonistic muscles are inhibited and there are two centers (a left and right) and the left one moves both eyes to the left and vice versa
This brainstem nucleus moves the eyeballs conjugately up or down involving synchronus excitation or inhibition of four muscles... where is it located? what parts does it consist of? what cranial nerve nuclei does it project to ?
the vertical gaze center AKA rostral interstitial nucleus of the MLF. found at the level of the superior colliculus (midbrain), consists of upward and downward parts, and projects to the occulomotor and trochlear nuclei
this nucleus directs convergence and divergence eye movements... what complex is it apart of? what is different about its tract compared to the other gaze centers' tracts?
perlia's nucleus AKA supraoculomotor area. the occulomotor complex, its fibers do not use the MLF
the brainstem centers for eye movement control two types of cells. What are they and what do they do?
burst cells fire rapidly and mediate saccadic eye movements and tonic cells fire more slowly and mediate slower smooth, pursuit or tracking movements
this nucleus is believed to integrate signals for saccadic movements to derive a new position signal that is sent to tonic cells.
nucleus prepositus hypoglossi
an occulomotor channel through the basal ganglia does what to eye movements? what is an example of one of these channels? the effect of the example is greatly enhanced in what condition?
suppresses or facilitates them; GABA neurons in the substantia nigra, pars reticulara that usually exert a tonic inhibitory effect on eye movements ceases fire during saccadic movement. Oculogyric crisis where the eyes are fixed upwards for long times is seen in parkinsonism from encephalitis
this part of the cortex is located in the middle frontal gyri and receives input from the visual cortex to direct voluntary rotation of both eyes... where do its fibers project?
frontal eye fields; fibers to the vertical and contralateral gaze centers and the ipsilateral superior colliculus
where is the visual association cortex located? what does it control? where do its fibers project too?
surrounds the primary visual cortex in the occipital lobe and includes parietal and temporal areas. it directs smooth pursuit
(tracking) movements mainly to the same side. to the lateral and vertical gaze centers and the superior colliculi.
conjugate eye movements involve what? vergent?
both eyes move in same direction; each eye moves in different direction
voluntary eye movements are classified as what? controlled by what? propagated by what cells? and the final position is held in place by what cells?
saccadic; frontal eye fields; burst cells; tonic cells
while saccadic movement occurs, the frontal eye fields receive input from the visual cortex. What can they do with this input?
they can utilize it or disregard it
the cortical reflex circuit does what? what areas of the brain does it use?
tracking a moving object by having the eyes lock onto that moving object. Uses the visual association cortex, parietal and temporal areas all integrated with the vestibular and flocculonodular signals.
the vestibulo-ocular reflex results from the stimulation of what causing the eyes to do what? what is this reflex used for clinically?
endolymph in the semicircular canals moves when the head is turned, causing the eyes to move in the opposite direction of the head rotation, this enables the eyes to remain fixed on a stationary object. used to evaluate brainstem injury in the unconscious patient
what is the optokinetic reflex? failure to elicit this reflex means what?
normal reflex induced by movement of the whole visual field across the retina AKA retinal slip. cortical lesion since it involves areas 18, 19 and the visual parietal and temporal areas
visual, auditory, and somatosensory reflexes are elicited subcortically via tracts to what? In terms of visual sensation, what is significant about this area?
the superior colliculi which have a retinotopic organization (contralateral) causing movement of the retina to that part stimulated.
the accomodation-convergence reflex is used for what? what are its three aspects?
for near vision; convergence (eyes rotate medially), accommodation (focus for near vision), and miosis (pupil becomes smaller to increase depth of focus)
what is seen with occulomotor nerve lesion?
external strabismus (extropia) and diplopia, ptosis (more than in horners), mydriasis (pupil dilation) and loss of pupillary light reflex, loss of accommodation-convergence reflex.
why is a lesion of the superior occulomotor nerve known as double elevator palsy?
bc that part of the nerve innervates the levator palpebrae superioris and the superior rectus
a painful occulomotor palsy involving the pupil is likely caused by what? a complete oculomotor palsy sparing the pupil? a partial oculomotor palsy sparing the pupil?
aneursym, diabetic neuropathy, and partial compression by aneurysm
what are the signs of a trochlear nerve lesion?
hypertropia, extortion, and vertical diplopia which is greatest when looking down. Pt. will usually tilt head to oppostie side of lesion
internal strabismus, diplopia, and tendency to turn the head to the side of the lesion are characteristics of a lesion where?
in the abducens nerve
a lesion to the abducens nucleus will produce what?
the same effects as a lesion to the abducens nerve and lateral gaze paralysis since the gaze center is also destroyed
this lesion is caused by transection of the MLF between Nu III and VI, may also be seen in MS, what is it and what are signs of it?
MLF-internuclear opthalmoplegia. no voluntary adduction, nystagmus in the abducting eye, and a normal accommodation-convergence reflex.
what is parinaud's syndrome? what may cause it? what are the normal signs of it?
lesion of the midbrain reticular formation; pinealoma or expanded suprapineal recesses from too much CSF; paralysis of upward gaze, loss of pupillary light reflexes and mydriasis, and impaired convergence.
an irritative (excitatory) lesion of the frontal eye fields results in what?
deviation of eyes to the opposite sides
a destructive lesion of the frontal eye fields results in what?
deviation of eyes to the side of the lesion and inability to voluntarily gaze to the opposite side.
lesions to the visual association cortex can cause what?
defective tracking and convergence movements
lesions to the vestibular nuclei cause what?
vertical, horizontl or rotational nystagmus. (lesions may be irritative or destructive)
lesions to the flocculonodular lobe may cause what?
loss of muscle coordination in vestibuloocular movements resulting in nystagmus and inaccurate eye movements.
what is heterotropia?
misalignment of the two eyeballs resulting in fatigue of the extraocular eye muscles. This results in cortical suppresion of the image of the defective eye and subsequent loss of visual acuity (amblyopia). This is permanent in aninfnt if it is not corrected within about six months.